The long and short of it...from simple matching, stacking, and building - to the exploration of basic math concepts such as big-little and half-whole - to more extensive learning about math and science principles such as fractions and equivalency - these blocks bring it all! Compatible with Unit Blocks and Giant Wooden Pattern Blocks. Large block is 5.5" long x 1.375" wide x .75" thick. Small block is 2.75" long. Set of 24 hardwood blocks - 12 of each size in rainbow colors.